Help with trust issues?

[fh]

so this girl and i are really close
we talk for hours everyday and are extremely alike.
she says all this great stuff about me, and she even talks about "us" having kids and doing stuff in the future.
shes even said that she loves me.
but the thing is, she lied to me in the past.
and i caught her flirting with guys over social media.
now i still do trust her, but i just question everything.
even if she tells me a hundred times that she doesnt care about any other guys, i still have a feeling that shes still flirting with them etc..
i want to be able to believe everything she tells me, but its extremely hard sometimes.
i have a feeling that my trust problems are going to ruin us eventually...
what can i do..