You're upset he only contacts you when his other lover is busy. Is he supposed to contact you when he's with them? If so, do you want him on the phone with them when he's with you?
I'm going to a party tonight with my partner, D. There is no way I'll check my messages when I'm with him. When I'm with him, I'm with him. When I go on my date tomorrow with Mr. and Mrs. Nice, I won't check my phone. I don't date people unless I give them my full attention. They deserve nothing less, or I wouldn't be with them.
So he doesn't love you. You can't make him love you. I'm a believer that loving is more important than being loved, since we can't control other people's emotions. We can spend our whole lives waiting for that very monogamy-oriented experience of being consumed by another individual's love and reciprocating, but it usually doesn't happen this way. And that's fine. It doesn't make love any less valid because it's so rarely evenly matched.