Is there a nice way to....

[OneTimeSBX]

i had this happen once. while we were at dinner i said "you know, i'm so glad i have friends like you that i can hang out with." it worked! turns out he did have a thing for me but my statement to him was so genuine and nice, we are still friends to this day.

[Scandia]

Be careful with saying "thank you for being such a good friend". If the person is obsessed with you and unhealthy, it can and will be misinterpreted. Most people will get the hint- especially when said as "we work so great as friends" or the sort. But some won't.