That is a clematis. The flowers look as though they have sustained slug damage, but that isn't the reason for their fading/falling off. This clematis is almost finished blooming, and the petals should fall off naturally at this stage. Notice that the entire flower doesn't fall, but only the petals. This is natural. The center will continue to grow, and will eventually form a seed head.
Also, the leaf damage looks like a curl rather than a wilt. This type of curl is generally caused by the piercing or sucking group of insects during plant growth. The first ones that come to mind are: spider mites, aphids, thrips, leafhoppers, scale insects, and tarnished plant bugs. Most general insecticides will be effective against these, but if you have scale, you will have to treat with a horticultural oil, in an attempt to suffocate the insects.
Those insects could also make the plant wilt. The fertilizer isn't the issue here. Look for insects on the plant. They will be very small, and depending on the species, they will move deep inside the plant when you disturb the foliage. Some insects, though, will remain on the undersides of the leaves, where they feed. Once you find an insect, you can choose how to treat from there.
For the slugs, I would recommend a trap rather than a poison/bait, because some slug poisons are toxic to birds, which may eat the slugs.
In general, your plant looks rather dense, which explains why parasitic insects would be attracted. Next winter, you could try to thin out the weak and unnecessary vines, to thin it out a little and increase air flow. The rain (which these insects hate) will also penetrate the plant better.