Calum Best is reportedly desperate to get back with on again/off-again GF Lindsay Lohan that he has promised to attend rehab to prove he is serious about the recently arrested for DUI ‘Mean Girls’ star.

“Calum first had the idea at Lindsay’s 21st birthday when he was watching her being so strong and staying away from alcohol,” says an insider.

“He still drinks – but obviously can’t do that around her anymore. And the way he feels at the moment, by her side is the only place he wants to be.”

If he does make it to rehab, Calum’s therapists are going to have a tough job on their hands since he has admitted to addictions to drugs, booze, sex and, of course, party-crazed starlets.