Unsure what to do
If I haven't talked to my sister in almost 6 months because of a sexual text message she sent my boyfriend should it be okay for the 2 of them to still call, text he would lie to me about it or not tell me. He even stayed at her house 3 separate times for a week at a time not answer his phone or call me. All because he needed to finish installing her stereo system. He says he started it and has to finish it or he'll look bad. Oh and when I found out he lied to me a few weeks ago I kicked him out and he now lives there. Mind you she's married but separated from her wife and supposedly has a boyfriend that she leaves to go see all the time.
It sounds like they're a couple.
As hurtful as this is, your borfriend is the one who was your partner and had the primary responsibility to be loyal to you. Your sister shouldn't sabotage your relationship, either, but she didn't choose to be your sister. Still stinks, though, and still wrong.
The situation has resolved itself, though, hasn't it? You kicked him out. He wasn't faithful to you, he probably won't be faithful to her, and she may be seeing someone else, anyway. I think she's not: I think the *story* that she's going out with another man is to convince you there's nothing going on.
The Geeks at the Big Box store don't require three weeks of overnights to install a stereo system. If this is your ex's source of income, he should find something he has talent for to earn a living.