If you're always thinking he's out messing around with some other girl when you can't get in touch with him you'll never want to touch him again. If you're going to be together forever you need to be in this thing together. If you need a monogamous relationship and he's not willing to provide he might not be the guy for you. Not being with other partners is part of being in a relationship. If he can't deal with it he shouldn't be in this thing.
Random sex is meaningless.
The longing to be with you physically is part of this thing. This is part of loving from afar. It's not easy. It sucks at times. It takes work.