Just keep going with fingering until you can fit more fingers in. Make sure you're moving your fingers up and down to try to widen the opening and pushing deeper if you can. Then get some toys and work on getting those in. Don't rely on him, have some solo time and get creative. But when he's there make sure you're getting a lot of oral too with the fingering. Spread it open so his tongue can make good contact with your clit. All this play and wetness will help you eventually get him all the way inside. But it's going to take time and a lot of play. Be patient and have fun.