I thought I played well, apparently not - Why is 11. ... c5(?) such a bad move?

(I did win this game eventually)

I played c5 with the idea that the queen must go back, and I will be able to gain space on the queen side and be able to put my bishop on b7. (Which is why I played 10. ... Bxd4?, also because I wanted to get all my pawns on dark square, and therefore my dark square bishop wouldn't do much)

c5 weakens the d6 pawn Rd1,Qd2 all win the pawn., Bb7 was possible without c5 right?

#2 Ya true, white is going to pile up on the d-file and attacking my d-pawn which will eventually fall, I missed that somehow.

Also, Bb7 was possible without playing c5, I thought it was better to kick out the queen and then play Bb7 and start trying to attack the e pawn, as well as getting more queenside space

@potatothing I think the most important thing to consider in a move are the short term and long terms costs and benefits.
Short term:
1. Queen is hit. This is useless. She simply moves and is not at all upset to have to do so.
Costs: No short term costs to speak of.
Long Term.
Benefits: More queenside space. This is a technical benefit, but considering that you don't have very many pieces, it isn't quite as useful as it could be.
1. d6 is now irreparably weak: There is simply nothing you can do about this. That pawn is sick and dying. This is a serious cost.
2. You have created a huge gap on d5 that can be used by a white piece to great effect. This also is unfixable and is a serious potential problem.
3. This is more advanced. Most players would not even consider this but it is worth thinking about.
You LOSE flexibility with your two most central pawns. The d6 pawn cannot move at all, and you gave away your plans for the c-pawn. Basically you froze the poor d6 pawn in place forever. Pawns like to be able to move, and any dreams he had of c6, Bb7 followed by a glorious d5 are gone now.

Consider this analysis, and tell me which is greater, the benefits or the costs.

#5 ya I see now, the d pawn is very weak and is basically a backwards pawn that I will have to suffer and spend time defending, while I won't be able to utilise my queen side space

Great analysis, thanks!