My [M16] girlfriend [F17] of 8months Is becoming less kind

we started out great and instantly connected, we were sexually active a lot and rarely argued, now in the last couple of months she started to become more bossy and sometimes rude. She also has been not as passionate to be intimate for a couple months, and the few times that we are intimate she looks and acts like she’s not fully into like before. Though she does constantly tells me that she loves me so much. I’m not sure that she does like before. Is this something that happens in all relationships? I love her and do not want to break up but rather solve the issue. Do not think that it is all bad- we are happy with each other most of the day and still have fun