trust on love

I love someone for 5 years,at first he didn't love me,he proposed me for time pass,with continue our relationship he did flirrt with another girls,but now he loves me somehow,but he breaked my trust in previous days,I love him so much & i want to spent my whole life with him but now i can't trust to him,i doubt him every time unless he do anything.....I want to trust him every time,but i can't........how can I overcome this problem??????how can I trust him?????????