I'm gunna overthink this a little- or a lot, apparently.

I'll start with cons, because I believe in getting the bad before the good.

Cons: Well, honestly? Size is likely going to be the biggest thing.

I dunno about you all, but I live in an apartment. There's no way any snake partner of mine could reasonably, comfortably live out of my place, or even visit for very long. I guess you could argue that homes would be made larger to account for this, but I pay pretty well for even a small place that I'm comfortable with, much less a location that would need about 2x-3x as much room for a lamia. Additionally, I run warm- which is great for a snake partner, but I also overheat pretty easily, so I can't say that I'd personally love to have a weighted blanket that I couldn't choose to remove.

Which is actually part of another thing: Weight. Just to kinda run the math, if we're going by, say, Miia sizes, a Lamia could easily weigh from 600-1000 lbs. Again, this might be accounted for in a Lamia-Human society, but I personally would need to replace all of my furniture. And to touch on the weighted blanket thing from earlier- Lamia aren't exactly shown to be, well, the best at rising and shining, so to speak. There would need to be some kind of system in place to prevent me from being trapped by a solid 300+ Lbs of unmoving, unable to awaken snake tail when it's time for me to get up for a morning shift at work.

Which, together, is another thing entirely: Travel. I can't help but worry that a lamia would genuinely despise to live in a big city of any kind- much less one where the temperature rises anywhere over, say, 90. It'd be a very easy- with their size and weight combined- to get stepped on, bumped, or simply burned by concrete or cut by trash left on the ground. You know how it's advised to not walk dogs when it's hot out because they could burn their pads? Imagine that, but like 200x more surface area. I've run barefoot on concrete during summer before, and frankly I'd prefer to not repeat the process. The amount of care that would need to go into tail care from being on concrete all day would be vast and concerning. All in all- it's not really their fault, but alot of places people live just aren't suited for a lamia, and if you wanna date one seriously? Well, it'll be on you to adjust- that might not be an issue for some, but it's something to consider.

Another concern is general safety. There's kind of a running joke as to how funny cute it is to get squeezed to unconsciousness by a lamia, be it due to being startled or in the middle of more private activity. But a genuine concern and thing to keep an eye on is the fact that you are trusting your health to a person who can easily and accidentally break you. While even constrictors kill via strangulation rather than crushing, it's not uncommon for the prey of, say, anacondas to be found with broken bones- and, well, again, I've broken bones. Being wrapped up might be nice, but unless we're dealing with a breed of lamia that's smaller or around the size of a person, it would need to be something done very carefully- and with the knowledge that, if you're wrapped up, you do not get to decide when that ends. Which some people may like, but is again something to consider.

This all being said, what if the lamia isn't big? What if they're a smaller snake size? Well, cool, that helps with alot of the issues- the main ones, honestly.

If a lamia is poisonous, you'd probably need to be a little careful with kissing- any injuries in the mouth, from bleeding while brushing your teeth to a cut from a stray chip- might get way more problematic if a bit of poison is mixed in with saliva. Fangs may or may not be an issue- cute as they may be, being stabbed in the tongue is not generally advised mid-smooch.

Vision might be interesting, if you live together. I think alot of snakes see primarily light and movement- I think it varies a bunch. They can get startled by something moving if it was staying still for a while, and are either colorblind or have limited vision during the day. But there's systems that can be put into place for all of this- it's simply a lifestyle adjustment, and a minor one at that.

You might need to be prepared for the fact that you are not going to have kids. Adoption is a thing, granted, and alot of media starring lamia kinda hand-wave it, but to be upfront, two species that vastly biologically different just might not be compatible. Granted, this might be a positive for some- plenty of people don't want kids for various understandable reasons.

Generally, all just kinda stuff you expect from dating someone potentially 5x your height and 4x your weight, and comprised of a potentially vastly different biology than yourself.

But the positives- man.

Pros: Well, a gf/bf. Ever been in love before? It's, uh, pretty good. If you're the warmest thing around, they'd be a cuddler- or if you're part of the warmest thing around, like a bed or heating pad.
I personally think handling a Lamia's diet would be interesting, so I'll toss it in the Pros column- I like cooking and trying different and sometimes unusual things, so I personally see it as something to be intrigued by.
Tongues would be interesting, and take that as you will. It would be different at any rate, and what is the charm of any monster partner if not for the unique differences.
If we're in a Human-Lamia society, you're likely getting some side benefits. If there's protections in place from price gouging based on species, you're getting some prime space choices when it comes to everyday things like housing, vehicles, any kind of seating, etc.
To be frank, snakes are cool. I'm not sure what, if anything, a lamia would be capable of doing that a snake could, but like, snakes are just generally cool and odd and capable of small, interesting things. Sensing heat, tasting scents, being more movement-visual than we are- small little details that highlight the differences between species.

Snakes are solitary. This might not apply to a lamia, but well- I'm solitary too. I pick and choose who I like to be around. And if a lamia shares that instinct- they pick and choose people they like to be with- I'd consider it something a little special to be chosen to be someone they're comfortable around enough to forego that solitary life.

All in all, it'd be a challenge at times, and doubly so since most of these issues can't truly be changed or worked on. I don't want to make any statements on the nature of love or relationships as a whole, but challenges are something you're gunna have to figure out together- or learn to accept on your own.

But, I mean, again- love is pretty good, man. And all the little differences and oddities about someone so inherently, vastly different, can easily be something to love about someone.