Why would he act like This??

[Zelda B]

I am insecure and nag my boyfriend alot.He makes me feel like this.But he has changed alot in his new job since he got a promotion, and wants to end our relationship soon if I don't get higher pay coz he wants marriage.He tells me this time and time again now.....he has started spending more times in the evening with his mate (who is gay) when he is with me he has a faraway look in his eyes,like he is thinking of something.He bought another mobile, the evenings he has started to go out he never answers till next day.He keeps his mobile on vibrate,won't answer his mates anymore when i am with him.Does this necessarily mean he is cheating? If so,with whom? and how would i catch him...