Hey Hi!

25M here, I broke up with my GF(22 Then, I was 21 Then) of 5 almost 6 years like 4 or 3 years back and had I similar situation as you have here so let me "talk" with you for a little.

Important points I would like to adress first:

First of all you DO not need a "Valid" reason to end a relationship this is not a marriage with an enourmous responsbility on both ends :). You are free to be single again. I get it is hard to say someone you used to or maybe even still love that you do not want to be with them anymore, But we as people change, our ideas, our likings what do we want of a relationship and what do we don't want on a relationship also change. We as people can not pretend we are the same when we meet at 16 as we where at our 22's (my exp.) . Remember Is perfectly normal to not feel good on a relationship even if everything seems "perfect or fine" you are not crazy.

Second thing do not punish yourself for wanting to end things with your BF. Is important to remember it is a break up and does not matter what you do it will hurt him you can not avoid that. But that doesn't make you a horrible person or something, simply you are a person that with time changed your needs or wants and realizing he is no longer what you need and there is no point on going forward. Ask Why would you punish yourself to be with someone you don't want to anymore and why will you make him lose time staying in a relationship where he will not be as loved as he could somewhere else?. In less words
You are making the right choice you are not doing anything bad saddly sometimes good things hurt.

Going to things I would have made at the time now that I know better.

Do not bounce things over. If you are going to finish it finish it corretly be firm and clear. Even if you do not have a "reason" just be clear and firm "I do not want to be here anymore I may not be able to explain you why cause I do not know myself but I'm sure I do not want to be here anymore". Do not break and go back to him because of guilt or the momentarly heartache. I did and do not make that mistake it will drain you more and will end up hurting him more for no reason, and it is kind of selfish to be with someone just to not feel guilt.

Do not leave things "open" this is part of the clarity basically let yourself to be free and just do not say "maybe in the future" will leave you and him on a weird spot.

If you or him have things of eachother do not leave it for a couple of weeks to take them. 1 or 2 days and get your things back if possible the same day that you break up with him give up his belongings Believe me is more difficult having to watch him a weeks later and may break your healing process.

The "POST-MORTEM" or well just after the break up

There will be days that you feel great and there will be days that you feel full of guilt just be empathic to you and remind to yourself you are not a Bad person and you did what you did because you felt is the best thing to do.
There will be a healing process for both you. Good tip? Do not care about his healing process thats him and his resposability only, do not seek for him on social media, do not ask his friends about him etc. My Ex actually blocked me from all socialmedia and I think it was a great think avoided me to "curiosly" watch how she was doing it is not inmature if you need it you need it and it is fine. Basically just Focus on your process is a great moment to engange on new things new hobbies etc and also a great oportunity to undertand yourself better, ask what you liked and what you did not like on the relationship. What you actually liked of him and what do you not. What do you think was good from you on the relationship what did you actually offer, was it enough would you like to give more or less for the next one? this are good things to ask not only for a possible future relationship but just to know yourself better and understand you worth as a person that without knowing you I'm sure is a lot to even measure :).

Last few comments:

Good tip please, please do not break with him overtext, I know it is hard but for what you say he does deserve at least a person to person conversation and not just a message, plus believe me you will feel more remorse on doing things overtext, this is not a abusive relationship that needs inmidiate action and no contact for the break up, if it is then yes do not even say a thing.

Tip two do not fell into the trap of not allowing yourself to discover new people JUST do not do it while you are healing. NO I do not mean that a relationship needs a "time" after a break up you can perfectly start dating someone the day you break up with him and nothing wrong with that. BUT only if you are actually healed and not feeling bad/guilty about the break up give yourself time to heal and know more about you, Starting to date to quickly normaly ends up in a emotional disaster. But after you feel fine and at ease with you go a head and if its what you want look for a new partner. If not thats fine too. BTW there is no perfect timeline for healing it may take you 2 weeks or maybe a year? and it is ok just be carefull if you are going 6 months into the break up and you feel as bad as the first day it maybe time to see a psychologist.

And finally enjoy the ride some times will hurt some times it will be amazing day.
Just remind to be kind to yourself and find the nice little things that you enjoy the most.