I just don't seem to hit it off with him.

hit it off with others
他人と仲良くやる

hit it off with someone really well
（人）と実に仲良くやっている［うまくいっている］

hit it off with someone right from the beginning
（人）と最初からそりが合う

not hit it off
肌［そり］が合わない

I just don't seem to hit it off with him.
彼とはとてもじゃないがうまが合いそうにない。

I just think you two could hit it off real well together.
私はあなたたち二人がとてもうまくやっていけると思う。