What is love? why do i feel this way?

im 16 hes 16 we've been together for 10 months. we have and we love each other. but sometimes i feel like i get bored with the relationship... and it takes a toll on both of us.. we used to fight and argue a lot a lot! over the dummest things...but now its a lot less fighting but we Still argue over stupid things. i love him and i wouldn't want to be with anybody else.some days i think about what it be like to be with another guy or him or himhappened makes me feel guilty and bad:( how do i stop 'that when my mind plays tricks on me? and sometimes i imagine about exes like what went wrong in past relationships what did i do what happpend so i can fix my problems and make sure i dont make them again. i think im loosing interest in him. weve been through soo much together. before him my relationships lasted 1-2 months he really does care about me. were super clingy with each other but we dont mind it. i support him an he usualy trys to support me. i jst think im loosing interest and im scared we might end it for sure. we always say we are when we fight but we always come back together<3 my parents wouldnt let us see each other for a long time because of the fighting so we snuck around for 5 months. now they know and let us see each other but.. im loosing interest and honestly were on the last last last string... please help me. do i really love him or do you think its lust. im trying to do everything to make me gain y happyness about us and life in general. i have depression and anxiety issues also idk if my meds are causing me to have littlw emotion or its cuz im loosing interest. i felt this way befoe and we got over it and i was happy again .the honeymoon stage is wayy over but idk if me not feeling all loveable eveyr day or barely ever is normal in a long relationship or not..like i said i felt this way before with him and we jst ignored it and focused on the little things and that helped a lot and we were happy again<3 i love him truely otherwise i would have left a long time ago... he actually stayed with me unliike the other boyfriends ie had they just left me and used me. i was gullable and stupid.... but im pretty sure i learned my mistakes an i wana keep this love lasting because its hard to find a guy like this in this day and time. please what do i do :'( sorry for typos im like really stressed and too lazy to fix them.