Yes, we can manifest love in our life. It requires action as much as it does Visualization, Affirmation, and a "Real Belief" in the outcome one wants. The mistake a lot of people make is they target a "specific person" instead of a "specific type" of person.
Simply visualize for instance receiving flowers at work with a signed card that professes their love, or waking up to breakfast in bed along with a greeting card or love note....etc While visualizing the event don't just see it in your mind but actually "Feel" the joy and happiness of the event. It is suggested you do this each night before going to bed and upon waking in the morning. Once again it's not about a "specific person" but rather a "specific type of person".
Probably the best way to start is to create (a profile) of your ideal mate listing their traits, hobbies, interests, type of occupation, member of clubs/organizations he/she might belong to, Charities they might support, neighborhood they live in, grocery store/department store they'd shop in,sports/artist or entertainers they'd follow or support, the type of church they attend, If they were to join an online dating site which one would it be.....etc
The next step is to imagine BEING this person. If you were them, "Would you want you?"
If the answer in your heart is "no" then you may decide that you need to make some changes. It's been said, "When we change, our circumstances change". Too many people ask for the moon but have very little to offer in return.
"Don't expect to sit next to the moon unless you are star!"
The last step is to (Be Where They Are).
Once you have the profile of your ideal mate you have to be willing to participate in the same types of activities, attend the same types of events,shop in stores (in their neighborhood) or travel to destinations you imagined him/her would. (If you aren't in the same circles of someone your odds of meeting them are slim) Opposites may attract in the short-term but it's Like that attracts Like for the long-term. Water tends to seek it's own level.
Best of luck!