How can i stop being so insecure and jealsous?

iv been with my boyfriend for a few yrs now nd we about to have our second child together im only nearly 18 myself and i love my boyfriend and family but i cant help bein jealous and insecure, i was already inecure before i got with him in terms of looks and nt really havin any confidence but nw its got out of hand and i know i need to sort it out. when we argue i know ppl say tings tey dnt mean but sometimes it just sticks he tells me im **** in bed compared to other ppl iv been wit, my body dosnt keep him interested cos iv had kids, im ugly and a slag and load more things upon them lines and he always tells me if im nt in the mood for sex he will get it of some one else and if i say it in retalliation he jus ses to me no one else will ever want me nd im lucky to ave n he dnt know y hes wit me he ses after that he dosnt mean these tings but then sometimes when we calm and just talkin he says nasty things as well hes really getting to me and makin me feel so horrible about myself i dnt even like to leave the house anymore cos hes said these tings so many times i think their true also i jus cnt excep hes had so many girlfriends partly cos he my first proper boyfriend and weneva ses said anything bout them it comes across like he thinks better of them than me even tho they cheated i love him wit all my heart and we have kids together and i dont want to throw all that away what do i do?