I'm hesitant to ask this OP, as seriously don't want to come over as dismissive or goady if you are for real - but ... ARE you for real?
Some ex b/f with substance abuse issues cheated on you multiple times, & you eventually split.
For whatever reasons, (I trust PP will get into these downthread) you elected to stay friends with him.
Last month, you enjoyed a shag with someone.
How is your sex life ANY business of his? He's just a friend. He's not your b/f. You have NOT slept with someone else - you have simply slept with someone. As you are at perfect liberty to do.
You are also at perfect liberty to not discuss your sex life with anyone at all, other than the person in your bed. You should CERTAINLY not have needed to tell your ex about it. It's none of his business!
Also ... "A gentlewoman never tells". I am actually a bit
about you disclosing this on behalf of your shagee ... you have no right to tell anyone else about his sex life!
Last month I was feeling very low and I slept with a friend of mine . I told him what happened as I feel so guilty, feel dirty and have ruined my friendship with the other guy and probably any hope of me and him getting back together.
Why did you have to be "feeling low" to allow yourself to shag your friend? Do you feel you needed to justify your decision to have sex? Why?
Are you playing into some kind of subconscious internalised Madonna/Whore Complex, whereby if you decline sex & stay 'chaste', that this will somehow earn you some brownie points & fate will 'reward' you by awarding you a renewed relationship with your Ex?
Can you not see how self-limiting & toxic that is?
Rightho. I know I'm peppering you with Q's here, & apologise if that feels intrusive to you - you have NO need to respond to me if you do not wish to.
But here's a final one:
Why, in the name of merry fuck, are you holding out for a boozy junkie who is a committed serial cheat?
Feel very upset probably lost two friends inside of a week
NEWSFLASH
Your Ex is NOT your friend. I am sure PP have already expounded on this. Believe them.
The friend you slept with? - I'm sure he's still your friend. Whether you decide to shag each other again, or not. There's simply no reason for him not to be ... other than you getting all weird over your Ex, who has not rights over your sex life & who - I cannot stress this enough OP - IS NOT YOUR FRIEND ANYWAY.
There you go! You're one nice shag up, & have not lost 2 friends.
You've simply found out that 1 of them never was, & 1 of them still is, plus possible ... benefits 