I've been with my ltr for about 4 months. she's in love with me and will do anything for me. the problem is, it seems like she's getting less interested in sex.

we still end up fucking nearly every time I see her, it's just that she doesn't seem excited during foreplay but once I start fucking her she becomes an animal. it's very weird, I don't know what can be the reason.

so pretty much -

she loves me she's willing to do anything she seems less interested in sex still gives me sex (but seems reluctantly) once we get it on, she loves it and doesn't want to stop

it almost appears as if it's duty sex since she knows she needs to fuck me to keep me. my questions are, is this normal?