Gfs mom that i kinda like but its wrong. Let me know what you guys think.

So im 24 and my girlfriend (21) her mom is 61 and shes definitely a milf or cougar or whatever it is. Shes not like pornstar hot but hot enough for me to sometimes be like i could get up in that if i was drunk or something but i would never cheat on my girlfriend i love her to much. Anyway ive been jerking off to her facebook for a couple weeks now and it feels good but like a good wrong if that makes sense. I know she likes me but i dont know in that way. What should i do?