Butterflylady... please don't give up.
My advice about trusting God would be, first, ask Him to help you trust Him. I don't really think that's something that you can do on your own.
Then, have a talk with Him and tell Him that you're leaving the whole situation in His hands. The guy, the despair, the lack of trust, all of it. Ask Him to take over, and give it totally to Him.
Spend as little time thinking about the guy as possible, and instead, try to keep your focus on Jesus. The peace that comes from that, is exactly what you need. Here are a few verses about it:
1 Peter 5:6-7 "Therefore humble yourselves under the mighty hand of God, that He may exalt you at the proper time, casting all your anxiety on Him, because He cares for you."
Psalm 55:22 "Cast your burden upon the LORD and He will sustain you; He will never allow the righteous to be shaken."
From Philippians 4: "The Lord is near. Be anxious for nothing, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. And the peace of God, which surpasses all comprehension, will guard your hearts and your minds in Christ Jesus.
Finally, brethren, whatever is true, whatever is honorable, whatever is right, whatever is pure, whatever is lovely, whatever is of good repute, if there is any excellence and if anything worthy of praise, dwell on these things. The things you have learned and received and heard and seen in me, practice these things, and the God of peace will be with you. "
Isaiah 26:3 "Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee"