I think you can. Some “loves” that have pas.sed will never fade away completely. One can keep a special place in you heart. But that doesn't mean you love the one you are going to marry with any less. You can love someone, eventhough you have loved (or still love, as you wish) someone else before.
I really loved my ex-boyfriend, and he will always have a place in my heart, but I'm very sure, I will ever love someone else enough to marry him (I don't know where I have to find the guy, but that's another problem
).