How long have you been seeing this girl? Is it true love and are you going to marry her. If not, then dump the girl and continue to train in both. Also, how old are you.
Since you seem a little new to all this, I’m going to assume that you are still kind of young. That’s a good thing. You can deffinitely do both MMA and lift. Girls are like trains. If you don’t care which one you ride, then you can always miss one. Another will be along in just a little bit.
Anyhow, you can rock evening MMA training if you get up in the morning to do your weights (more likely conditioning). Making time in the morning is the key. But if you’re not down with that then shitty for you. Figure out how many hours you have for training and allot them accordingly.