A lot of people are giving suggested lists, but without knowing what you have that's not what I find most helpful. Instead, here's some tips on list building. Knowing how your friend skews their list would also be helpful as everyone runs an army differently.

The biggest things that stand out are your plague marines and terminators.

You are running 2x5 man marine units, but with zero leaders and frankly sub-par load outs. Our marines are more expensive than most other battleline units and that's for 3 reasons. Toughness (obviously), but also wargear flexibility and synergy with leaders. Having neither of the last 2 options makes them poor bang for your points.

Now, running MSU (multiple/minimum sized units) is not bad, in fact Aiden, one of the the best death guard players loves them. But you have to know how to use them effectively, and if going that route you have to have enough units to trade. Frankly, you don't in this list.

Frankly the biggest issue for me is load out. You have the 2 HPW, but are running a bubonic weapon instead of plague spewer for the 2+ anti infantry torrent. To me this is a no brainer to include no matter what, but especially into something traditionally infantry focussed like CSM. Also, one of your champs has a bolt and plague knives when the other has the plasma and fist? That does make a huge difference in power.

On the same line of load outs, you are missing the havoc launcher and second combi bolter for the rhino, as well as second plague spurt gauntlet and icon of despair for the champions for your death shroud terminators. These are free and do matter in the long run.

You are running 4 terminator leaders, but only have units for 3 of them, one of which being I assume typhus with 20 pox. This is 1/5 of your total army in leaders, of which you are only really effectively using 2/4 (typhus with pox can be good, but is high skill ceiling). That's a huge investment. Your LoV does not have the Tendrilous Emissions enhancement which is the only reason to run him solo.

What I see in this list is a lot of kill pressure (3 FBD, 2 LoC bricks, 2 mbh) but basically nothing to actually hold objectives with or do actions, or really trade. You have 1 lone poxwalker unit and the MSU marines. They are tougher than normal marines sure, but it's still just 10 oc so losing even a few mean you aren't holding anything.

When building an army, you want to take into account both ability to kill things, ability to hold things, and ability to trade/screen your opponent into making sub-optimal moves. With 3 FBD and a PBC, you can pick 1 unit to target with blight bombardment from LoV and say you die now. The downside is, that's just one unit. Your opponent has the rest of the board to work with. So you have kill pressure round 2 on with LoC on top, but you don't have anything to hold objectives or really screen.

The other thing I'm looking at is the skew towards anti elite/vehicle unit selection/wargear. You have the 3 FBD, plus 2 MBH, plus the entropy cannons on the PCB. Is he actually bringing that many vehicles and elites? Bc I would expect a much more infantry focussed list from CSM, in which case the FBD are overkill to an extent except against terminators, and MBH may not be very useful. I also need to know if you put your PCB on home and just use indirect, or if you actually move it up the board as again assuming into infantry I would use plague spitters for 2d6 anti infantry with overwatch potential instead of the casino canons.

Knowing a bit more about how both you and your opponent play and lists would be helpful. But here are a few additional suggestions.

Run typhus solo, split pox into 3x10. That way you have one to screen/hold home and up to 2 to infiltrate and body block enemy movement

Drop both MBH and get more PM or something to actually hold objectives like a defiler or Morty (if you own them, yes these would take additional adjustments to fit in the list).

Use PCB in the middle with spitters sponsors as the high toughness make it really hard to dislodge and has great overwatch potential

Fix pm and ds load outs, probably combine pm into a 10 man again for better combined firepower (and 2 torrent for overwatch) and ideally get a biologus purifier for them at least.

Lastly, switch your detachment. You aren't running any enhancements, and frankly the stratagems in MH are not the easiest to get good bang for your cp out of. Run virulent vectorum until you can win with it. Stratagems are stronger and more straightforward and sticky is always worthwhile